1. Field of Invention
This invention relates to Hall thrusters that are used in propulsion systems. Specifically, this invention relates to systems and methods that allow for the extensions in the useful lifetimes of Hall thrusters.
2. Description of Related Art
A Hall thruster is an electric propulsion device used principally for spacecraft propulsion. Hall thrusters rely on an annular ceramic discharge channel in which plasma is ionized and accelerated. The plasma is accelerated by a combined operation of axial electric and magnetic fields applied in the coaxial channel. Hall thrusters provide ion velocities in the range of 10 km/s to 35 km/s, with current densities, about 0.1 A/cm2. The input power levels for most thrusters are in the general range of 0.5 kW to 10 kW.
While most Hall thrusters retain the same basic design, the specific details vary with the nominal operating parameters, such as the working gas, the gas flow rate and the discharge voltage. The general design parameters that are varied to meet specific requirements include the discharge channel geometry, the channel material, and the magnetic field distribution. The discharge channel is typically made of boron nitride, but other compositions are possible.
During normal use, the interaction between the plasma and the discharge channel results in erosion of the downstream edge of the channel, ultimately resulting in erosion of the surrounding magnetic system. The operational lifetime of Hall thrusters is determined by the amount of time the thruster can operate before the magnetic system is damaged by exposure to the plasma within the channel. The lifetime of state-of-the-art Hall thrusters is on the order of 10,000 hours. Thus, if there was a means of ensuring that the magnetic system is not exposed by erosion of the ceramic discharge channel, then the useful lifetime of a Hall thruster could be extended.
Several methods have been employed in the prior art to increase Hall thruster lifetime. Attempts have been made to identify and incorporate discharge chamber materials with high resistance to erosion. Prior techniques for extending operational lifetime include increasing the thickness of the discharge channel material, magnetically shielding the discharge channel material from the plasma, and controlling the energy of the plasma interacting with the discharge channel.
However, none of the prior techniques implemented have eliminated the life limiting mechanism of Hall thrusters. Additionally, some of the prior techniques introduced negative effects on thruster performance. Thus, there is a need in the prior art to have Hall thrusters with increased usable lifetimes.